When an automobile collides with a pedestrian, it is very likely that the automobile may knock him off and cause his head to be struck against its hood. If the hood is deformed downwardly, it absorbs the energy of the collision effectively and thereby protecting the pedestrian.
It is often the case, however, that a reduction in size of an automobile or any requirement made thereof from a design standpoint makes it necessary to have its engine located immediately below its hood in close proximity thereto. As a result, the hood has only a small room for deflection. Various proposals have, therefore, been made to cope with the situation. A couple of examples are described in JP-A-2003-285768 and JP-A-2003-191865, respectively.
JP-A-2003-285768 discloses an automobile hood 100 as shown in FIG. 7 hereof. The hood 100 is composed of a hood skin 101, a hood frame 102 attached to the underside of the hood skin 101, a plurality of flanges 104 attached along an opening 103 defined by the hood frame 102 and each having a substantially S-shaped cross section and a flange 105 situated in the center of the opening 103 and having a substantially S-shaped cross section.
When an external force acts on the center of the hood skin 101 as shown by an arrow in FIG. 7, the flanges 104 and 105 are deformed as shown by imaginary lines and allow the hood skin 101 to be bent downward as shown by imaginary lines.
FIG. 8 hereof shows the stroke of deformation of the hood 100 in relation to the load acting on it. A study made by the present inventors indicates that as the hood 100 is so constructed that its steel flanges 104 and 105 and its steel hood skin 101 may be plastically deformable, the load acting on it marks a peak in the beginning and drops thereafter with the progress of its buckling. As its absorption of impact energy is proportional to the load acting on it, its performance in absorbing impact energy becomes lower after its peak. Accordingly, it is desirable to explore a structure having an impact energy absorbing performance which does not become lower even after the peak of the load acting on it.
JP-A-2003-191865 discloses an automobile hood as shown in FIG. 9. The hood 110 is shown upside down for convenience of explanation and has a hood skin 111, a hood frame 112 attached to the hood skin 111 and a plurality of conical dimples 113 protruding from the hood frame 112 to the hood skin 111. The dimples 113 are plastically deformable to absorb impact energy.
The dimples 113 are, however, effective only when an external force resulting from the collision of the automobile acts on that part of the hood skin 111 under which one of the dimples is situated, and the hood does not provide any impact energy absorbing performance as desired when the external force acts on the hood skin between any two adjoining dimples 113. Accordingly, it is desirable to explore a structure having the same impact energy absorbing performance whichever part thereof may receive an external force as a result of the collision of the automobile.